Good questions. Atmos metadata is attached to Dolby TrueHD 7.1 tracks on disc. If the processor/receiver supports Atmos, the display and/or info screen will show Atmos. No channel input info will be shown and dashes will be in the place of channel numbers when Atmos metadata is recognized. If no height or virtual height speakers are in use in a system, Atmos metadata is lost and the TrueHD 7.1 disc track is played without it and channel number information returns and usually displays as 3/4/1. Atmos output is designed to accommodate different speaker arrangements and try to achieve object placement as well as it can with a given system.
Atmos support is all over the place for sure. It can be supported well or not. I remember as a kid thinking anything with a "Turbo" badge must be fast and awesome. Then, I drove an 84 VW Rabbit Turbo Diesel.
The 84 Renault Fuego wasn't better by much.
They weren't as peppy or fun as the 84 Datsun 300ZX Turbo was, that's for sure.